Osteoporosis is a prevalent disease in aging humans which results in a net loss of skeletal tissue. Since there is no satisfactory therapeutic treatment for osteoporosis, it is important to increase our understanding of the complex etiology of the disease with the aim of preventing its occurrence. Experiments are planned to investigate the interaction of diet, physical exercise and steroid hormones on the development of senile osteoporosis in animals. Studies will be carried out to elucidate the effect of the intake of dietary phosphate and calcium and the calcium: phosphate ratio on the development of osteoporosis in aging mice subjected to forced exercise. Studies will also be conducted to evaluate the influence of estrogen therapy on bone resorption induced by high dietary phosphorus in ovariectomized adult rats.